jess (n.)

leg-strap used in hawking and falconry, mid-14c., from Old French jes "straps fastened round the legs of a falcon," plural of jet, literally "a cast of a hawk, a throw, a throwing," from Latin iactus "a throw, a cast," from iacere "to throw, cast" (from PIE root *ye- "to throw, impel"). Related: Jesses.